1287693 (1) 玖、發明說明 【發明所屬之技術領域】 本發明大體上係有關於極短波長反射式微影系統，及 更特定地係有關於在遠紫外線（EUV)微影系統中漫射性地 反射電磁幅射。 【先前技術】 微影術爲用來產生特徵結構於基材的表面上的一種處 理。微影術在電腦晶片製造的領域中是一種習知的處理。 一種電腦晶片經常被用到的基材爲半導體材質，如矽或砷 化鎵。在微影期間，一位在一微影工具內的一平台上的半 導體晶圓會被曝光在由一曝光系統投射於該晶圓表面上的 一影像下。該曝光系統典型地包括一光罩（又被稱爲罩幕） 用來將電路特徵的影像投射到該晶圓上。 該光罩大體上係位在該半導體晶圓與一光源之間。該 光罩通常是位在該微影工具內的一光罩台上且典型地被用 作爲將一電路印在一半導體晶片上的光學罩幕。一光源通 過該罩幕照射，然後通過可將該影像縮小的一系列光學鏡 片。這一小的影像然後被投射到該半導體晶圓上。該處理 與使用在照像機上的處理，其將光曲折以形成一影像於攝 影底片上，相類似。 光線在平板印刷處理中扮演一主要的角色。例如，在 微處理器的製造中，產生更強大的微處理器的一個關鍵即 在於縮小使用在該微影成像處理中的光線的波長。一較短 - 4- 1287693 (2) 的波長可製造較小的裝置。較小的裝置可讓更多的電晶體 及其它的電路元件被蝕刻到一單一矽晶圓上，而得到功能 更強，更快的裝置。 然而，持續地將波長變短對於晶片製造已產生了多項 挑戰。例如，光線的波長愈短會讓更多的光線被用來將光 線聚焦的光學玻璃所吸收。此一現象的結果爲，某些光線 無法到達該矽晶圓，導致一不良的電路圖案被形成在該矽 晶圓上。當波長接近約11-14奈米（nanometer，nm)的遠 紫外線區時，玻璃材質會變得更具吸收性。對於在此區域 內的微影成像（被稱爲遠紫外線微影（EUVL))而言，玻璃鏡 片被反射鏡所取代，且該光學系統爲反射式而非繞射式。 EUV照射光束的品質的測量問題在EUVL應用中是一 持續的問題。使用錯位干涉測量法是光學系統分析的一個 傳統方法。在繞射光學系統中使用錯位干涉測量法是習知 的。對於一反射式光學系統而言，如使用在EUVL中者， 則會產生許多問題。例如，在某些應用中（如波前診斷）， 錯位干涉測量法需要一在該EUV範圍內的一漫射光源。 傳統的繞射光漫射器並不在這麼短的波長工作。因此，建 構一可在EUVL系統的極短波長下操作之反射式電磁幅射 漫射器是很被需要的。 【發明內容】 本發明係關於一種反射式電磁幅射漫射器其可在極短 波長，如EUVL系統中使用者，下使用。 1287693 (3) 本發明的一個實施例包含一被製造在一基材上的反射 式電磁幅射漫射器。該漫射器包含一結構其具有獨立栅格 單元的三維度輪廓，一高反射性的塗裝被形成在該輪廓 上。該反射性塗裝大體上採用在其底下之該三維度輪廓的 外形。一吸收性的光柵接著被製造在該反射性塗裝上。因 爲在光柵底下之獨立柵格單元的三維度輪廓的關係，所以 光柵間距將會漫射性地反射電磁幅射。光柵的吸收性會將 照射到其上之其餘的電磁幅射吸收掉。該光栅因而變成一 特殊化的隆奇（Ronchi)刻度，其可被使用在極短波長反射 式微影系統中之波前評估及其它光學診斷上。 一種用來製造一電磁幅射漫射器的方法亦被揭示。一 基材被提供，一個具有獨立的柵格單元之三維度的輪廓製 造。一反射性塗裝接著被形成在該三維度輪廓上使得該反 射性塗裝大體上順應該輪廓的外形。一吸收性的光柵被形 成在該反射性塗裝上。該吸收性光柵讓光學診斷，如隆奇 測試，被實施於該入射的波前上。 本發明之額外的特徵及優點將在下文中加以說明，且 部分從說明中將會是很明顯的，或可從本發明的實做中學 到。本發明的優點將可從結構上被瞭解及在文字敘述中及 申請專利範圍中以及在附圖中被特別地指出。 應被瞭解的是，前述的一般性說明及以下的詳細說明 都是舉例性及說明性的，且是爲了提供本發明的進一步解 說0 1287693 (4) 【實施方式】 現將參照本發明的實施例詳細說明，這些實施例係被 示於附圖中。 第1圖顯示一代表性的微影成像系統1 〇〇的一部分。 系統1 00係以系統測試結構被顯示。一光源1 05提供電磁 幅射至該照射鏡片1 1 0。在此舉例性的EUV實施例中， 照射鏡片是反射性的，因爲EUV波長是非常的短。照射 鏡片110將電磁幅射聚焦在一位在光罩平面120上之光罩 台（未示出）上。一光罩台（未示出）一般是用來在微影期間 固持該光罩。一光源模組115被安裝在該光罩平面120上 來取代光罩安裝於光罩平台上。這對於最初的系統啓動而 言是較佳的。 在此測試結構中，被設置在該光源模組1 1 5上之本發 明的電磁幅射漫射器150是位在光罩平面120上。投射鏡 片130可包括一入射光瞳122及一出射光瞳124及帶有一 光瞳平面126，如圖所示。一感應器模組140被設置在該 晶圓平面上。應被瞭解的是，電磁幅射漫射器1 5 0在 EUV系統中是反射式的，這與在較長的波長（如深紫外線 或可見光）下操作且光罩是透射式的微影成像系統不相 同。 在本發明的一實施例中，其上疊置有吸收性光柵的電 磁幅射漫射器1 5 0可如一特殊的隆奇（R ο n c h i)光柵般作 用。隆奇測試是一種習知的光學系統測試方法。在隆奇測 試中，一光束被聚焦於一正在被測試的光學系統中的焦點 -7- 1287693 (5) t用以測試其像差繞射光柵（隆奇光柵）被放置成與位在該 焦點附近的該光軸垂直，其將入射的光束分裂成數個繞射 級°該等繞射級彼此獨立地前進且被一光瞳中繼鏡片（在 一反射式系統中的反射鏡）所收集，其在測試時會在觀察 平面上形成該物件的一出射光瞳影像。在該測試結構的舉 例性實施例中，該觀察平面係位在該晶圓平面1 3 5後方。 第2圖爲顯示一隆奇型光柵210，其可被應用在依據 本發明的一實施例的電磁幅射漫射器150上。第3A-3 B 圖I顯示當錯位干涉測量被實施於一光學系統，如光學系統 1 00，中以進行一隆奇測試時的一所想要的結果。 如第2圖所示，在一較佳的實施例中，該隆奇光柵 210爲 3.2微米寬且每6.4微米即重複（如，光柵週期 d = 6.4微米）。光柵210與一位在晶圓表面135上的該感應 器模組1 40上的錯位光柵結合。在該光源模組1 1 5上的該 隆奇型光柵210被投射鏡片130成像在晶圓平面135的一 類似的錯位光栅上。如第3A圖所示，一光柵相對於另一 光柵的相對對齊產生一錯位干涉圖3 1 0，其具有與在波前 中的誤差坡度成正比之強度條紋。光柵之相對運動會產生 一隨時間而變的相位級階式的錯位干涉。此運動可藉由電 腦來控制光罩或晶圓台兩者中的一者或兩者來實施。該干 涉圖案3 1 0具有條紋可見度函數3 2 0，如第3 B圖所示。 該條紋可見度或相關性分布函數是由一隆奇光柵刻度 (ruling)的富利葉轉換（Fourier transform)來提供。波峰代 表的是條紋對比最高的區域。參見LC· Wyant發表在期 1287693 (6) 刊Applied Optics於1974年一月發行第13冊第200-202 頁題目爲”White Light Extended Source Shearing Interferometer”的文章。繞射級是由光線的路徑長度所決 定的。例如，在一第一級最大値中，每一光線的路徑長度 跟與其相鄰的光線的路徑長度相差±—個波長。在一第三 級最大値中，每一光線的路徑長度跟與其相鄰的光線的路 徑長度相差±三個波長。 爲了要測量波前，光罩台相對於晶圓台被移動或晶圓 台相對於該光罩台被移動用以產生相位級階其會以受控制 的方式來改變該干涉圖案310。一位在該感應器模組140 底下或之上的CCD偵測器（未示出）接收並測量被透射的 幅射。該光源模組1 1 5然後可被該光罩台移動用以將一不 同的繞射光柵放置在光學路徑上，用以用該光源模組光柵 2 1 0的一正交的方位來測量波前。光學系統的診斷測試可 由這些觀察來實施。 由於該反射試照射鏡片的獨特特徵的關係，所以在一 波前中之刻面（facet)的發生是在極短波長環境中，如一 EUVL系統，會遇到的一個問題。例如，在入射光瞳122 處的波前可能被刻面化。依據所使用的光源，將會是被黑 暗區域所包圍之照射波峰的一分散式的陣列。例如，一大 體積的光源會產生被等大的黑暗區所隔開來之大的刻面。 當光源體積變小使，照射刻面相對於介於其間之黑暗區的 尺寸亦會隨之變小。在這兩種情形中，刻面都被均勻地分 佈在該光瞳上。熟悉波前測量及錯位干涉的人而言很明顯 -9- 1287693 (7) 的是，此一刻面化的波前對於錯位干涉圖案3 1 0會有負面 的影響。在感應器模組1 40處的光線強度將會是不均勻 的。這些刻面如果未加以改正的話，將擴及該干涉圖案 3 10，並影響到條紋可見度函數320的訊號對雜訊（SNR)比 率。這對於錯位干涉處理會有一不利的影響。 一刻面化的波前的問題可藉由使用一位在光罩平面上 的漫射反射器（漫射器）來克服。漫射電磁幅射是被改變方 向或被散射的幅射使其被均勻地散布在波前。因此，即使 是該照射系統產生一刻面化的波前，用一依據本發明的電 磁幅射漫射器來改變方向及散射即可讓該入射光瞳被均勻 地塡滿。在入射照明的數値孔徑（ΝΑ)低於投射鏡片的數値 孔徑的情形中，漫射反射仍可確保適當的光瞳塡充。實際 上，本發明採用該照明源的ΝΑ作爲該錯位干涉的要求。 第4Α圖顯示一依據本發明的電磁幅射漫射器的剖面 圖460。第4Β圖顯示獨立的柵格單元450的頂視圖470。 一具有獨立的柵格單元的三維度輪廓的結構400被製造在 一基材410的表面上。該等獨立的柵格單元450(亦被稱 爲級階）在該基材上一被稱爲空的（null)基材平面420的預 定範圍上具有一變化的高度。在一實施例中，高度是在製 造之前被隨機地選定’然後使用像是電子束微影的技術形 成在基材400上。已知的演算法則可被用來數學地決定或 計算每一柵格單兀450的隨機輪廓高度。形成波峰及波谷 輪廓之被隨機地選定的級階高度以隨機化的結構4〇〇來顯 不。如在此較佳的貫5也例中所述的，該隨機化的結構4 〇 〇 1287693 (8) 可被類比至一三維度的柵格或棋盤，其中每一方格的高度 或深度係隨機地變化或依照一預先選定的演算法則而變 化。此一形成在基材4 1 0上之被控制的結構4 0 0形成該電 磁幅射漫射器的基礎。 在一較佳的實施例中，該等獨立的級階45 0的高度範 圍是該空的基材平面42 0 ±25奈米。因此，從最低的級階 到最高的級階的高度範圍約爲5 0奈米。每一獨立的級階 450的面積約100奈米XI 00奈米。如第5圖所示的，一 漫射器板500的面積約400微米X4 00微米。較佳實施例 的特定結構對於短波長EUVL系統而言是獨一無二的。在 較長的波長時，此舉例性的結構將會呈現完全的平滑且不 會將入射的電磁幅射漫射。 特別重要的兩個參數爲將被漫射的電磁幅射的波長及 所需要的角漫射量。這些參數決定獨立的級階450的平均 面積，以及控制在該結構的三維度輪廓中的隨機變化的或 然率分布。根據這些參數，一熟悉此技藝者在瞭解本文所 提供的說明之後將能夠使用此技藝中已知的技術來設計任 何數量之不同的三維度柵格形結構。 具有安排成柵格形式之波峰及波谷輪廓的多層表面 400的製造可透過多種方法來完成。結構400可被直接形 成在基材410的頂面（即，第一表面）上。例如，一連串的 圖案-及-蝕刻步驟被實施，其中級階的高度的控制是由蝕 刻時間的掌握來完成。在使用這些方法中，N個圖案-及-蝕刻步驟可產生2〜層。或者’一或多層可被形成在第一 -11 - 1287693 (9) 基材4 1 0上，且結構4 Ο 0可被形成在該一或多層中。自然 蝕刻深度控制可藉由首先沉積一由具有良好的相爲蝕刻選 擇性特性的兩種材質所組成的多層來獲得。在被沉積的多 層中的層數應大於或等於在最終結構中所需要的層數，及 每一層的厚度應能滿足所需要的級階高度變化。利用多層 的一舉例性製造方法被揭示在授予N a u 11 e a u的美國專利 第 6,3 92,792B 號中。 一較佳的製造方法使用單一圖案級階，其涉及了將複 數層輪廓圖案直接刻寫在光阻上，該光阻然後被用作爲該 隨機化的結構4 0 0的一穩定的基材。理想的光阻材質是非 常平滑，用以降低來自於該反射塗裝的散射。例如，氫 silsesquiozane (HSQ)光阻具有低於 lnm rms之可達的粗 縫度。HSQ是由設在美國密西根州 Midland市的 Dow Corning公司所製造。 一高度反射性的塗裝430藉由蒸發或其它已知的技術 而被形成在該結構400的三維度輪廓上。此塗裝可由能夠 在EUV範圍內反射電磁幅射的物質，如鉬/矽（MoSi)，來 製造。MoSi可使用已知的磁控管濺鍍技術來沉積。該反 射性塗裝43 0大體上順應該結構400的波峰及波谷輪廓的 形狀。入射電磁幅射因而可被漫射性地反射離開該表面。 熟悉此技藝者可瞭解的是，結構400的該三維度輪廓的某 些平滑將會因爲該反射性塗裝43 0而發生。 一吸收性塗裝440接著被形成在該反射性塗層430的 一部分上用以產生一光柵5 05。根據該吸收性塗裝440的 1287693 (10) 厚度，其將會順應底下的反射性塗裝43 0的形狀。然而， 上文提及之相對於該反射性塗裝43 0的平滑效果因爲相對 大的特徵尺寸（如第5圖所示），所以對於該吸收性塗裝 440而言已不再是一項考量。 如第5圖所示，該吸收性塗裝440以一光柵或一條帶 式圖案的形式被施加且只在該反射塗裝430的一特定部分 上。被該光柵所覆蓋的該反射塗裝43 0部分與所想要的光 柵5 05特徵有關。示於第4圖中的側視圖460顯示該漫射 器被吸收性光栅505所覆蓋的部分。所使用的吸收性材質 爲氮化矽，其被作得夠厚用以吸收入射於其上的電磁幅 射。 第5圖顯示其上疊置吸收性光柵440的一漫射器板 5 00的放大結構。一或多片漫射器板5 00可被安裝在光源 模組1 1 5上用以構成電磁幅射漫射板1 5 0。兩片帶有被正 交地定向的吸收性光柵5 05之分離的漫射器板500被示 出。在一實施例中，該吸收性光柵5 0 5約3.2微米寬且每 6.4微米即重複，因此讓介於光柵之間的反射空間成爲 3.2微米寬。在另一實施例中，該吸收性光柵5 05具有一 約6.4微米的寬度且約12.8微米即重複，因此讓介於光 柵5 05之間的反射空間成爲6.4微米寬。熟悉此技藝者將 可瞭解到，光柵的尺寸及週期性與將被實施之測試的特殊 需求有關。例如，光柵的尺寸可由一特殊測試所需求的錯 位量來決定。不同尺寸的光柵可在不偏離本發明的精神與 範圍下被實施。 -13- 1287693 (11) 吸收性光柵5 05典型地被對角線地定向橫跨該隨機化 的結構400且典型地延伸橫跨整個漫射器板5 00。如圖所 示，在吸收性光柵5 05之間存有反射區，由於位在其底下 之該隨機化的結構400的波峰及波谷輪廓的關係，所以其 可漫射式地反射電磁幅射。該光栅的方向及尺寸不僅與但 磁幅射的波長有關，還與使用在錯位干涉中的其它參數有 關，這是熟悉此技藝者所能瞭解的。 以上所揭示的結果爲一被工程設計之可在EUV波長 疵操作的反射式電磁幅射漫射器1 5 0。疊置在該漫射器板 5 00上的是一吸收性光栅5 05，其可如一特殊化的隆奇刻 度般地作用，以使用在極端波長平板印刷系統中，如 EU V L系統。參照回第1圖，來自光源1 0 5的電磁幅射被 提供給光源模組1 1 5。光源模組1 1 5包含一電磁幅射漫射 器150其包括一或多個漫射器板500。電磁幅射將會被漫 射性地反射到投射鏡片130，且吸收性光柵5 05的一沒有 刻面影像將會出現在感應器模組1 40處以進行錯位干涉測 量法的波前分析。該干涉圖310可在許多光學診斷中被使 用。 在另一實施例中，該吸收性光柵5 05可被省略掉。在 此實施例中，該結構400之帶有反射塗裝43 0的柵格式波 峰及波谷輪廓將會如一電磁幅射漫射器般作用，其可被使 用在對EUV光的漫射源有需要的地方。 第6圖顯示製造本發明的電磁幅射漫射器板5 00的方 法（步驟6 1 0-6 3 0)。漫射器板500被形成在一基材上。典 1287693 (12) 型地，此基材爲一半導體材質，如矽或砷化鎵。 在步驟6 1 0，具有獨立的柵格單元之三維度結構被製 造在該基材上。如上文所述，該多層的表面可利用熟悉此 技藝者所習知的多種方法來達成。例如，一連串的圖案_ 及-蝕刻步驟可被使用在一多層基材上’以及將多層輪廓 直接刻寫在一單一的光阻層上。在一實施例中，該等獨立 的柵格單元的厚度是在一約50奈米的預定範圍內被隨機 地選取。用於隨機高度選擇之特定的演算法則與將被漫射 性地反射的幅射的波長有關。波長愈短，獨立的柵格單元 的可用高度範圍就愈窄。在EUV幅射被漫射的一較佳的 實施例中，用於獨立的栅格單元之預定的範圍爲50nm。 熟悉相關領域的人將能夠產生一演算法則來符合上述的要 件。 在步驟620，一反射性塗裝被形成在獨立的柵格單元 的三維度輪廓上。該反射性塗裝接著被形成在獨立的柵格 單元之該三維度輪廓上使得該反射性塗裝大體上順應該輪 廓的外形。對於euv幅射而言，該反射性塗裝可以是矽化 鉬（MoSi)。MoSi係使用習知的技術，如磁控管濺鑛，而 被沉積在該波峰及波谷輪廓上。 最後，在步驟63 0，一吸收性光柵被形成在該反射性 塗裝上，最好是沿著該三維度柵格的一對角線。·該吸收性 光柵的尺度會依據將被寳施的光學診斷的特殊需要而改 變。在一使用在EUV錯位干涉測量的較佳實施例中，該 光柵的吸收部分約爲3.2微米寬且約每6.4微米即重複。 -15- 1287693 (13) 氮化矽爲一般用作爲吸收性塗裝的材質。 應被瞭解的是，雖然以上的說明主要係以使用反射性 光學元件（如，光源模組1 15及感應器模組140)的EUV微 影系統爲例’但本發明可等效地被運用在使用於微影系統 中的其它波長上，其中該微影系統具有適當的透射/折射 構件取代反射構件。 熟悉此技藝者將可瞭解的是，在不偏由隨附的申請專 利範圍所界定之離本發明的精神與範圍之下可達成許多形 式及細節上的變化。因此，本發明的範圍不應被侷限在上 文中所述的任何一個被舉例的實施例上，而應是由以下的 申請專利範圍及其等效物來界定。 【圖式簡單說明】 爲了要顯示本發明之舉例性的實施例而被包括在本說 明書中之附圖構成本說明書的一部分，且顯示出本發明的 實施例並與文字說明一起解說本發明的原理。相同的標號 代表相同的構件，標號中的第一個數字代表該構件第一次 出現的圖號。 第1圖顯示一具有依據本發明的一實施例之漫射器的 微影成像系統的一部分。 第2圖顯示一舉例性的隆奇（Ronchi)光柵。 第3 A及3 B圖顯示一所想要的錯位干涉測量結果。 第4A及4B圖顯示隨機化結構波峰及波谷輪廓的實 施例的兩個視圖。 -16- 1287693 (14) 第5圖顯示一具有用來錯位干涉測量的光柵之電磁幅 射漫射器的實施例。 第6圖顯示製造依據本發明的漫射器的方法。 主要元件對照表 100 微 影 成 像 系 統 105 光 源 110 照 射 鏡 片 120 光 罩 平 面 115 光 源 模 組 130 投 射 鏡 片 135 晶 圓 平 面 150 電 磁 幅 射 漫 射 器 122 入 射 光 瞳 124 出 射 光 瞳 126 中 間 光 瞳 平 面 140 感 應 器 模 組 2 10 隆 奇 型 光 柵 3 10 錯 位 干 涉 圖 320 條 紋 可 見 度 函 數 460 剖 面 圖 470 頂 視 圖 450 獨 的 柵 格 單 元 400 結 構1287693 (1) Field of the Invention The present invention relates generally to extremely short wavelength reflective lithography systems, and more particularly to diffuseness in extreme ultraviolet (EUV) lithography systems. The ground reflects electromagnetic radiation. [Prior Art] Microphotography is a process used to create a feature on the surface of a substrate. Microlithography is a well-known process in the field of computer wafer fabrication. A substrate on which a computer chip is often used is a semiconductor material such as germanium or gallium arsenide. During lithography, a semiconductor wafer on a platform within a lithography tool is exposed to an image projected by an exposure system onto the surface of the wafer. The exposure system typically includes a reticle (also known as a mask) for projecting images of circuit features onto the wafer. The reticle is substantially tethered between the semiconductor wafer and a light source. The reticle is typically positioned on a reticle stage within the lithography tool and is typically used as an optical mask for printing a circuit onto a semiconductor wafer. A light source is illuminated through the mask and then passed through a series of optical lenses that reduce the image. This small image is then projected onto the semiconductor wafer. This process is similar to the process used on a camera, which bends the light to form an image on a film negative. Light plays a major role in lithographic processing. For example, in the manufacture of microprocessors, one of the keys to producing a more powerful microprocessor is to reduce the wavelength of the light used in the lithographic imaging process. A shorter - 4- 1287693 (2) wavelength allows for smaller devices. Smaller devices allow more transistors and other circuit components to be etched onto a single germanium wafer for a more powerful and faster device. However, continually shortening the wavelength has created several challenges for wafer fabrication. For example, the shorter the wavelength of the light, the more light will be absorbed by the optical glass that focuses the light. As a result of this phenomenon, some of the light cannot reach the germanium wafer, resulting in a poor circuit pattern being formed on the germanium wafer. When the wavelength is close to the far ultraviolet region of about 11-14 nanometers (nm), the glass material becomes more absorbent. For lithographic imaging in this region (known as Far Ultraviolet Vision (EUVL)), the glass lens is replaced by a mirror that is reflective rather than diffractive. The measurement of the quality of EUV illumination beams is a continuing problem in EUVL applications. The use of misalignment interferometry is a traditional method of optical system analysis. The use of misalignment interferometry in diffractive optical systems is conventional. For a reflective optical system, if used in the EUVL, many problems arise. For example, in some applications (such as wavefront diagnostics), misalignment interferometry requires a diffuse source of light within the EUV range. Conventional diffracted light diffusers do not work at such short wavelengths. Therefore, it is highly desirable to construct a reflective electromagnetic radiation diffuser that can operate at very short wavelengths of the EUVL system. SUMMARY OF THE INVENTION The present invention is directed to a reflective electromagnetic radiation diffuser that can be used in very short wavelengths, such as in EUVL systems. 1287693 (3) An embodiment of the invention comprises a reflective electromagnetic radiation diffuser fabricated on a substrate. The diffuser comprises a structure having a three-dimensional profile with individual grid cells on which a highly reflective coating is formed. The reflective coating generally adopts the shape of the three-dimensional profile underneath. An absorptive grating is then fabricated on the reflective coating. Because of the three-dimensional profile of the individual grid cells underneath the grating, the grating spacing will diffusely reflect the electromagnetic radiation. The absorptivity of the grating absorbs the remaining electromagnetic radiation that is incident on it. The grating thus becomes a specialized Ronchi scale that can be used for wavefront evaluation and other optical diagnostics in very short wavelength reflective lithography systems. A method for fabricating an electromagnetic radiation diffuser is also disclosed. A substrate is provided, a three-dimensional profile with independent grid cells. A reflective coating is then formed over the three dimensional profile such that the reflective coating substantially conforms to the contoured profile. An absorptive grating is formed on the reflective coating. The absorptive grating allows optical diagnostics, such as the Longch test, to be performed on the incident wavefront. The additional features and advantages of the invention will be set forth in part in the description in the description. The advantages of the invention will be apparent from the description of the appended claims and appended claims. It is to be understood that the foregoing general description and the following detailed description of exemplary embodiments of the invention DETAILED DESCRIPTION OF THE INVENTION These embodiments are shown in the drawings. Figure 1 shows a portion of a representative lithography imaging system 1 . System 100 is displayed in a system test structure. A light source 105 provides electromagnetic radiation to the illumination lens 110. In this exemplary EUV embodiment, the illuminating lens is reflective because the EUV wavelength is very short. The illuminating lens 110 focuses the electromagnetic radiation on a reticle stage (not shown) on the reticle plane 120. A reticle stage (not shown) is typically used to hold the reticle during lithography. A light source module 115 is mounted on the reticle plane 120 instead of the reticle mounted on the reticle stage. This is preferred for the initial system startup. In this test configuration, the electromagnetic radiation diffuser 150 of the present invention disposed on the light source module 115 is positioned on the reticle plane 120. Projection mirror 130 can include an entrance pupil 122 and an exit pupil 124 and an aperture plane 126 as shown. A sensor module 140 is disposed on the wafer plane. It should be understood that the electromagnetic radiation diffuser 150 is reflective in the EUV system, which operates with longer wavelengths (such as deep ultraviolet or visible light) and the reticle is transmissive lithography. The system is different. In an embodiment of the invention, the electromagnetic radiation diffuser 150 on which the absorptive grating is superposed can function as a special R ο n c h i grating. The Longch test is a well-known optical system test method. In the Longch test, a beam is focused on a focal point in the optical system being tested - 7287693 (5) t to test its aberration diffraction grating (longge grating) placed in position The optical axis near the focus is perpendicular, which splits the incident beam into several diffraction orders. The diffraction stages advance independently of one another and are collected by a stop relay lens (mirror in a reflective system) When it is tested, an exit pupil image of the object is formed on the observation plane. In an exemplary embodiment of the test structure, the viewing plane is positioned behind the wafer plane 135. Figure 2 is a diagram showing a gallo-type grating 210 that can be applied to an electromagnetic radiation diffuser 150 in accordance with an embodiment of the present invention. 3A-3B Figure I shows a desired result when misalignment interferometry is performed in an optical system, such as optical system 100, to perform a Ronchi test. As shown in Fig. 2, in a preferred embodiment, the ridge grating 210 is 3.2 microns wide and repeats every 6.4 microns (e.g., grating period d = 6.4 microns). The grating 210 is coupled to a misaligned grating on the sensor module 140 on the wafer surface 135. The gallo-type grating 210 on the light source module 115 is imaged by a projection lens 130 on a similar misalignment grating of the wafer plane 135. As shown in Fig. 3A, the relative alignment of one grating relative to the other produces a misaligned interferogram 310, which has intensity fringes proportional to the slope of the error in the wavefront. The relative motion of the grating produces a phase-order stepped misalignment that varies with time. This motion can be implemented by the computer controlling one or both of the reticle or wafer table. The interference pattern 3 1 0 has a fringe visibility function 3 2 0 as shown in Fig. 3B. The fringe visibility or correlation distribution function is provided by a Fourier transform ruling Fourier transform. The crest represents the area with the highest contrast of stripes. See LC·Wyant, published in 1287693 (6), published in January 1974 by Applied Optics, Vol. 13, pp. 200-202, entitled "White Light Extended Source Shearing Interferometer". The diffraction level is determined by the path length of the light. For example, in a first stage maximum 値, the path length of each ray is different from the path length of the ray adjacent to it by ± one wavelength. In a third-order maximum 値, the path length of each ray is different from the path length of the light adjacent to it by ± three wavelengths. In order to measure the wavefront, the reticle stage is moved relative to the wafer stage or the wafer stage is moved relative to the reticle stage to produce a phase step which changes the interference pattern 310 in a controlled manner. A CCD detector (not shown) under or above the sensor module 140 receives and measures the transmitted radiation. The light source module 1 15 can then be moved by the reticle stage to place a different diffraction grating on the optical path for measuring the wave with an orthogonal orientation of the light source module grating 2 1 0 before. Diagnostic tests for optical systems can be implemented from these observations. Due to the unique characteristics of the reflective illumination lens, the occurrence of facets in a wavefront is a problem encountered in very short wavelength environments, such as an EUVL system. For example, the wavefront at the entrance pupil 122 may be faceted. Depending on the source used, it will be a decentralized array of illumination peaks surrounded by dark areas. For example, a large volume of light source produces a large facet that is separated by a large dark area. As the volume of the light source becomes smaller, the size of the illuminated facet relative to the dark zone in between will also decrease. In both cases, the facets are evenly distributed over the pupil. It is obvious to those familiar with wavefront measurement and misalignment interference -9- 1287693 (7) that this facet wavefront has a negative effect on the misalignment interference pattern 3 1 0. The intensity of the light at the sensor module 140 will be uneven. These facets, if not corrected, will extend the interference pattern 3 10 and affect the signal-to-noise (SNR) ratio of the fringe visibility function 320. This has an adverse effect on the misalignment interference processing. A faceted wavefront problem can be overcome by using a diffuse reflector (diffuser) on the reticle plane. The diffuse electromagnetic radiation is a redirected or scattered radiation that is evenly spread over the wavefront. Thus, even if the illumination system produces a faceted wavefront, the incident pupil is uniformly filled by a direction and scattering using an electromagnetic radiation diffuser in accordance with the present invention. In the case where the number of apertures (ΝΑ) of the incident illumination is lower than the number of apertures of the projection lens, the diffuse reflection still ensures proper optical charging. In practice, the present invention uses the enthalpy of the illumination source as a requirement for the misalignment interference. Figure 4 shows a cross-sectional view 460 of an electromagnetic radiation diffuser in accordance with the present invention. The fourth diagram shows a top view 470 of the individual grid cells 450. A structure 400 having a three-dimensional profile of individual grid cells is fabricated on the surface of a substrate 410. The individual grid cells 450 (also referred to as steps) have a varying height over a predetermined range of substrates referred to as a null substrate plane 420. In one embodiment, the height is randomly selected prior to fabrication and then formed on substrate 400 using techniques such as electron beam lithography. Known algorithms can then be used to mathematically determine or calculate the random contour height of each grid unit 450. The randomly selected step heights that form the peaks and troughs are shown in a randomized structure. As described in the preferred example, the randomized structure 4 〇〇1287693 (8) can be analogized to a three-dimensional grid or checkerboard in which the height or depth of each square is random. The ground changes or changes according to a pre-selected algorithm. The controlled structure 40 formed on the substrate 410 forms the basis of the electromagnetic radiation diffuser. In a preferred embodiment, the height of the independent steps 45 0 is 42 0 ± 25 nm of the empty substrate plane. Therefore, the height range from the lowest level to the highest level is about 50 nm. The area of each individual step 450 is approximately 100 nm XI 00 nm. As shown in Fig. 5, a diffuser plate 500 has an area of about 400 microns X 4 00 microns. The particular structure of the preferred embodiment is unique to short wavelength EUVL systems. At longer wavelengths, this exemplary structure will appear completely smooth and will not diffuse incident electromagnetic radiation. Two parameters that are particularly important are the wavelength of the electromagnetic radiation to be diffused and the required angular diffusion. These parameters determine the average area of the independent steps 450 and the probability distribution of random variations in the three-dimensional profile of the structure. Based on these parameters, one skilled in the art will be able to design any number of different three-dimensional grid-like structures using techniques known in the art, after understanding the description provided herein. The fabrication of a multi-layered surface 400 having peaks and trough profiles arranged in a grid form can be accomplished in a variety of ways. Structure 400 can be formed directly on the top surface (i.e., the first surface) of substrate 410. For example, a series of pattern-and-etch steps are performed in which the control of the height of the steps is accomplished by mastering the etching time. In using these methods, N pattern-and-etch steps can produce 2~ layers. Alternatively, one or more layers may be formed on the first -11 - 1287693 (9) substrate 410, and the structure Ο 0 may be formed in the one or more layers. Natural etch depth control can be obtained by first depositing a plurality of layers of two materials having good phase etch selectivity characteristics. The number of layers in the deposited plurality of layers should be greater than or equal to the number of layers required in the final structure, and the thickness of each layer should be such as to satisfy the desired level height variation. An exemplary manufacturing method utilizing multiple layers is disclosed in U.S. Patent No. 6,3,92,792, issued to U.S. A preferred method of fabrication uses a single pattern level, which involves directing a complex layer outline pattern directly onto the photoresist, which is then used as a stable substrate for the randomized structure 400. The ideal photoresist material is very smooth to reduce scattering from the reflective coating. For example, hydrogen silsesquiozane (HSQ) photoresists have a coarseness of less than 1 nm rms. HSQ is manufactured by Dow Corning, Inc., Midland, Michigan, USA. A highly reflective coating 430 is formed on the three dimensional profile of the structure 400 by evaporation or other known techniques. This coating can be made of a material capable of reflecting electromagnetic radiation in the EUV range, such as molybdenum/niobium (MoSi). MoSi can be deposited using known magnetron sputtering techniques. The reflective coating 43 0 generally conforms to the shape of the peaks and trough profiles of the structure 400. The incident electromagnetic radiation can thus be diffusely reflected off the surface. It will be appreciated by those skilled in the art that some smoothing of the three dimensional profile of structure 400 will occur due to the reflective coating 430. An absorptive coating 440 is then formed over a portion of the reflective coating 430 to produce a grating 505. Depending on the thickness of the 1287693 (10) of the absorbent coating 440, it will conform to the shape of the underlying reflective coating 430. However, the smoothing effect mentioned above with respect to the reflective coating 430 is no longer a term for the absorptive coating 440 because of the relatively large feature size (as shown in Figure 5). Consideration. As shown in Fig. 5, the absorptive coating 440 is applied in the form of a grating or a strip pattern and only on a particular portion of the reflective coating 430. The portion of the reflective coating 43 0 covered by the grating is associated with the desired features of the grating 505. Side view 460, shown in Figure 4, shows the portion of the diffuser that is covered by the absorptive grating 505. The absorptive material used is tantalum nitride, which is made thick enough to absorb the electromagnetic radiation incident thereon. Fig. 5 shows an enlarged structure of a diffuser plate 500 on which the absorptive grating 440 is superposed. One or more diffuser plates 500 can be mounted on the light source module 115 to form an electromagnetic radiation diffusing plate 150. Two separate diffuser plates 500 with the orthogonally oriented absorptive gratings 505 are shown. In one embodiment, the absorptive grating 500 is about 3.2 microns wide and repeats every 6.4 microns, thus allowing the reflective space between the gratings to be 3.2 microns wide. In another embodiment, the absorptive grating 506 has a width of about 6.4 microns and repeats about 12.8 microns, thus allowing the reflective space between the gratings 505 to be 6.4 microns wide. Those skilled in the art will appreciate that the size and periodicity of the grating is related to the particular needs of the test to be performed. For example, the size of the grating can be determined by the amount of misalignment required for a particular test. Different sized gratings can be implemented without departing from the spirit and scope of the invention. - 13 - 1287693 (11) The absorptive grating 5 05 is typically diagonally oriented across the randomized structure 400 and typically extends across the entire diffuser plate 500. As shown, there is a reflective region between the absorptive gratings 505, which reflects the electromagnetic radiation diffusely due to the relationship between the peaks and trough profiles of the randomized structure 400 underneath. The direction and size of the grating are not only related to the wavelength of the magnetic radiation, but also to other parameters used in misalignment interference, as will be appreciated by those skilled in the art. The result disclosed above is an engineered electromagnetic radiation diffuser 150 that is engineered to operate at EUV wavelengths. Overlaid on the diffuser plate 500 is an absorptive grating 505 which acts as a specialized singularity for use in extreme wavelength lithography systems, such as the EU V L system. Referring back to Fig. 1, the electromagnetic radiation from the light source 105 is supplied to the light source module 1 15 . Light source module 1 15 includes an electromagnetic radiation diffuser 150 that includes one or more diffuser plates 500. The electromagnetic radiation will be diffusely reflected to the projection lens 130, and a non-faceted image of the absorptive grating 05 will appear at the sensor module 140 for wavefront analysis of the misaligned interference measurement. The interferogram 310 can be used in many optical diagnostics. In another embodiment, the absorptive grating 505 can be omitted. In this embodiment, the grid-like crests and trough profiles of the structure 400 with reflective coatings 43 will function as an electromagnetic radiation diffuser, which can be used in the need for diffusing sources of EUV light. The place. Fig. 6 shows a method of manufacturing the electromagnetic radiation diffuser plate 500 of the present invention (step 6 1 0-6 30). A diffuser plate 500 is formed on a substrate. In the type 1287693 (12), the substrate is a semiconductor material such as germanium or gallium arsenide. At step 610, a three-dimensional structure having individual grid cells is fabricated on the substrate. As noted above, the surface of the multilayer can be achieved using a variety of methods known to those skilled in the art. For example, a series of pattern _ and - etching steps can be used on a multi-layer substrate ' and the multi-layer outline can be directly written on a single photoresist layer. In one embodiment, the thickness of the individual grid cells is randomly selected within a predetermined range of about 50 nanometers. The particular algorithm used for random height selection is related to the wavelength of the radiation that will be reflected diffusely. The shorter the wavelength, the narrower the available height range of the individual grid cells. In a preferred embodiment in which EUV radiation is diffused, the predetermined range for the individual grid cells is 50 nm. Those familiar with the field will be able to generate an algorithm to meet the above requirements. At step 620, a reflective coating is formed on the three-dimensional contour of the individual grid cells. The reflective coating is then formed on the three dimensional profile of the individual grid cells such that the reflective coating substantially conforms to the contour of the profile. For euv radiation, the reflective coating can be molybdenum molybdenum (MoSi). MoSi is deposited on the peak and trough profiles using conventional techniques, such as magnetron sputtering. Finally, at step 63 0, an absorptive grating is formed on the reflective coating, preferably along a diagonal line of the three-dimensional grid. • The dimensions of the absorptive grating will vary depending on the particular needs of the optical diagnostics that will be performed by Posh. In a preferred embodiment for use in EUV misalignment interferometry, the absorbing portion of the grating is about 3.2 microns wide and repeats about every 6.4 microns. -15- 1287693 (13) Tantalum nitride is a material commonly used for absorptive coating. It should be understood that although the above description mainly uses an EUV lithography system using reflective optical elements (for example, the light source module 151 and the sensor module 140) as an example, the present invention can be equally applied. At other wavelengths used in lithography systems, where the lithography system has suitable transmissive/refractive members in place of the reflective members. It will be appreciated by those skilled in the art that many changes in form and detail can be made without departing from the spirit and scope of the invention. Therefore, the scope of the invention should not be limited to any of the exemplified embodiments described above, but should be defined by the following claims and their equivalents. BRIEF DESCRIPTION OF THE DRAWINGS In order to illustrate exemplary embodiments of the present invention, the drawings included in the specification constitute a part of the specification, and illustrate embodiments of the invention and together with the description principle. The same reference numerals denote the same components, and the first digit in the number indicates the first occurrence of the component. Figure 1 shows a portion of a lithography imaging system having a diffuser in accordance with an embodiment of the present invention. Figure 2 shows an exemplary Ronchi grating. Figures 3A and 3B show a desired misalignment measurement. Figures 4A and 4B show two views of an embodiment of a randomized structure peak and trough profile. -16- 1287693 (14) Figure 5 shows an embodiment of an electromagnetic radiation diffuser having a grating for misaligned interferometry. Figure 6 shows a method of making a diffuser in accordance with the present invention. Main component comparison table 100 lithography imaging system 105 light source 110 illumination lens 120 reticle plane 115 light source module 130 projection lens 135 wafer plane 150 electromagnetic radiation diffuser 122 entrance pupil 124 exit pupil 126 intermediate pupil plane 140 Sensor Module 2 10 Longch-type Grating 3 10 Displacement Interferogram 320 Stripe Visibility Function 460 Sectional View 470 Top View 450 Unique Grid Unit 400 Structure
-17- 1287693 (15) 4 10 基 材 420 空 的 基 材 平面 500 漫 射 器 板 430 反 射 性 塗 裝 505 光 柵 440 吸 收 性 塗 裝-17- 1287693 (15) 4 10 Base material 420 Empty base material Plane 500 diffuser plate 430 Reflective coating 505 Photo grating 440 Absorbing coating
-18--18-